U.S. patent number 6,821,623 [Application Number 10/135,498] was granted by the patent office on 2004-11-23 for recycled rubber products.
This patent grant is currently assigned to Ryvec, Inc.. Invention is credited to Peter Kvesic.
United States Patent |
6,821,623 |
Kvesic |
November 23, 2004 |
Recycled rubber products
Abstract
Recycled rubber products are made in a two step process. In the
first step, ground rubber is treated with a polyurethane binder to
make a treated rubber. In the second step, the treated rubber is
mixed with additional polyurethane binder and molded into finished
products. This method uses less polyurethane binder than the
conventional process, but the products have higher tensile
strengths. The molding time is also reduced because of the reduced
amount of polyurethane binder used.
Inventors: |
Kvesic; Peter (Elmira, OR) |
Assignee: |
Ryvec, Inc. (Anaheim,
CA)
|
Family
ID: |
29249470 |
Appl.
No.: |
10/135,498 |
Filed: |
April 29, 2002 |
Current U.S.
Class: |
428/407; 427/222;
427/322; 427/407.1 |
Current CPC
Class: |
C08L
19/003 (20130101); C08L 75/04 (20130101); C08L
19/003 (20130101); C08L 75/04 (20130101); Y10T
428/2982 (20150115); Y10T 428/2998 (20150115); C08L
2666/14 (20130101); C08L 2666/08 (20130101) |
Current International
Class: |
C08L
19/00 (20060101); C08L 75/04 (20060101); C08L
75/00 (20060101); B32B 005/16 (); B05D
003/00 () |
Field of
Search: |
;427/222,322,407.1
;428/407 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Le; H. Thi
Attorney, Agent or Firm: Knobbe Martens Olson & Bear
LLP
Claims
What is claimed is:
1. A method of making recycled rubber products with less
polyurethane binder reduced curing times, and high tensile
strengths compared with equivalent products made by known
polyurethane binder methods, the method comprising a treatment step
comprising mixing ground rubber with a first polyurethane binder
until the first polyurethane binder is reacted and the rubber is
free of clumps, and a forming step comprising mixing the product of
the treatment step with a second polyurethane binder and molding
the resulting mixture.
2. The method of claim 1 using from about 0.25% to about 1.5% by
weight of the first polyurethane binder.
3. The method of claim 2 comprising about 1% by weight of the first
polyurethane binder.
4. The method of claim 1 wherein the treatment step is performed at
an elevated temperature.
5. The method of claim 1 wherein the treatment step is performed at
about 150.degree. F.
6. The method of claim 1 wherein the first polyurethane binder is
the same as the second polyurethane binder.
7. The method of claim 1 wherein the first polyurethane binder is
different from the second polyurethane binder.
8. The method of claim 1 comprising from about 1% to about 3% by
weight of the second polyurethane binder.
9. The method of claim 1 wherein the molding is performed at from
about 200.degree. F. to about 400.degree. F.
10. The method of claim 1 wherein the molding is performed at from
about 75 psi to about 500 psi.
11. The method of claim 1 wherein the treatment step further
comprises mixing a dye or pigment with the ground rubber and the
first polyurethane binder.
12. The method of claim 1 wherein the forming step further
comprises mixing a dye or pigment with the ground rubber and the
second polyurethane binder.
13. The method of claim 1 wherein the ground rubber contains
nylon.
14. A method of making a composite of ground rubber and
polyurethane comprising preparing a treated rubber by mixing ground
rubber with a first polyurethane binder at an elevated temperature
until the first polyurethane binder is reacted and the rubber is
free of clumps, and mixing the treated rubber with a second
polyurethane binder and molding the resulting mixture at elevated
temperature and pressure.
15. A recycled rubber product with less polyurethane binder,
reduced curing time, and high tensile strength compared with
equivalent products made by known polyurethane binder methods, made
by a method comprising a treatment step comprising mixing ground
rubber with a first polyurethane binder until the first
polyurethane binder is reacted and the rubber is free of clumps,
and a forming step comprising mixing the product of the treatment
step with a second polyurethane binder and molding the resulting
mixture.
16. Polyurethane treated rubber particles comprising rubber
particles coated with a cured polyurethane binder, wherein the
treated rubber particles comprise from about 0.25% to about 1.5% by
weight of the polyurethane binder.
17. The treated rubber particles of claim 16 further comprising a
pigment or dye.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to recycled rubber products and
more particularly to composites made from ground rubber particles
and polyurethane binders.
2. Description of the Related Art
Old tires and other rubber articles may be ground into rubber
particles suitable for recycling. This ground rubber is also known
as crumb rubber. At the present time in the United States, Canada,
and Mexico, over 20 million pounds of recycled rubber are used each
month. Recycled rubber is used to produce many finished goods,
including welcome mats, animal mats, truck-bed liner mats,
playground mats, speed bumps, railroad crossing pads, running
tracks, and bases for traffic control devices. Presently, finished
goods produced from recycled rubber are made by either vulcanizing
the rubber or by making composites using ground rubber and
polyurethane binders.
In the vulcanizing process, the rubber is first dried to reduce the
water content to less than 0.5%. The rubber is then vulcanized with
sulfur. In some cases, the rubber is first treated to give a
product with higher tensile strength. Rubber treated for
vulcanization cannot be used in the polyurethane binder
process.
Many types of binders are used in the polyurethane binder process.
The terms "polyurethane binder" and "binder" are used
interchangeably herein. The cost of these binders ranges from about
$0.70 per pound to about $1.40 per pound. In the commercial
process, the ground rubber is mixed with from about 3% to 20% of
the binder, and the mixture is molded into the finished product.
The process may be run under a variety of conditions, for example
high heat and high pressure or low heat and low pressure. Dry
rubber, rubber containing less than 0.5% water, is desirable, but
not necessary. A finished product made with rubber with a high
water content has lower tensile strength than one made with dry
rubber, however. Most commercial crumb rubber contains more than 1%
water, and few manufacturers dry the rubber.
SUMMARY OF THE INVENTION
The preferred embodiments of the invention provide methods of
making composites from ground rubber and polyurethane binders. In
one aspect, such methods use less binder than the conventional
polyurethane binder method, while providing products having high
tensile strengths. The reduced amount of binder also reduces the
curing time.
A second embodiment relates to a method of treating rubber
particles with polyurethane. These treated rubber particles are
used to make molded composite products.
A third embodiment relates to recycled rubber products made from
ground rubber and polyurethane binders. These products have high
tensile strength compared to similar products made with the
conventional process using the same proportion of rubber and
binder.
A fourth embodiment relates to polyurethane-coated rubber
particles. Additional binder may be added to these coated or
treated rubber particles to make recycled rubber products. A
pigment or dye may be added in the coating step to make colored
rubber particles. These particles are also suitable for loose-fill
applications.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used herein, the term "binder" means "polyurethane binder."
Unless otherwise indicated, all percentages are by weight.
Preferred methods have at least two steps. First, a treatment step
in which the ground rubber is treated with a polyurethane binder.
This first step is called "coating" or "treating" the rubber. The
product of this first step is called "coated" or "treated" rubber.
In a second step, a forming step, the treated rubber is mixed with
additional polyurethane binder and molded into finished
products.
Typically, the rubber comes from car, truck, or tractor tires, but
any type of rubber may be used. The rubber is ground to a size of
between about 8 mesh to about 40 mesh depending on the finished
product desired. The ground rubber can be used with or without
nylon cord content, but is preferably free of metal content.
Any type of polyurethane binder suitable for rubber applications
may be used in the preferred process, for example one-part,
two-part, or latex binders. Some binders comprise extenders and are
more economical. In cold-cure processes, 100% polyurethane binders
are preferred. Binders may be selected for particular properties,
such as reaction characteristics, hardness, and the like.
Optimizing binder selection is well known in the art, such that
binder selection optimization in accordance with the preferred
embodiments may be performed in view of the disclosure herein
without undue experimentation.
The first or treatment step does not require dry rubber. The ground
rubber is mixed with from about 0.25% to about 1.5% of a
polyurethane binder until the binder is reacted and the rubber is
free of clumps. In a preferred embodiment, about 1% of the binder
is used. Substantially any binder may be used in this step.
Suitable binders for rubber applications are well known in the art,
for example MD-400 and MD-403 binders (Ryvec, Inc., Anaheim,
Calif.), and may be used in accordance with the preferred
embodiments. Preferably, a fast reaction binder is used in this
step. A dye or pigment may optionally be added in this step to
color the rubber.
Mixing may be performed from ambient temperature to about
300.degree. F. for from about 1 minute to about 3 hours. Higher
temperatures typically require shorter mixing times, and vice
versa. For example, using 1% binder, the mixing time at ambient
temperature, 100.degree. F., 150.degree. F., and 200.degree. F. is
about 2 hours, about 1 hour, about 15 minutes, and about 8 minutes,
respectively. Preferably, the mixing is performed from about
100.degree. F. to about 200.degree. F. for from 5 minutes to about
30 minutes. Suitable mixing means are well known in the art, for
example, high-speed mixers, ribbon mixers, mixer-extruders, mortar
mixers, and the like. High-speed mixers can generate temperatures
up to about 180.degree. F. without additional heating. Mortar
mixers are preferably jacketed. Preferably, a ribbon mixer is used.
More preferably, the ribbon mixer is equipped with a double spiral
ribbon (a double ribbon mixer). Even more preferably, the double
ribbon mixer is jacketed. Ribbon mixers are available in a range of
sizes. The speed of a ribbon mixer ranges from about 50 rpm to
about 120 rpm. The preferred speed depends on the width of the
paddles, with wider paddles requiring slower speeds for equivalent
mixing results. Optimizing the mixing conditions is within the
scope of the skilled artisan in view of the disclosure herein.
In the second or forming step, the treated rubber from the first
step is mixed with additional binder, and the mixture is molded
into finished products. The forming step is similar to the
commercial process except that treated rubber in used instead of
untreated rubber. Accordingly, performing and optimizing the
forming step is within the scope of the skilled artisan in view of
the disclosure herein.
Substantially any type of binder may be used in the forming step.
Selecting suitable binders is well known in the art. Preferably,
from about 1% to 3% binder is used in this step. The binder used in
this step may be the same or different from the binder used in the
first step. A dye or pigment may optionally be added in this step.
As in the treatment step, any type of mixer known in the art may be
used in the forming step, for example, high-speed mixers, ribbon
mixers, mixer-extruders, mortar mixers, and the like. The treated
rubber, binder, and optional pigment is mixed until substantially
uniform, typically, about one minute. Typically, the resulting
mixture is then placed into a mold, by weight or by volume, and
leveled.
Molding may be performed at a variety of temperatures and
pressures, as is well known in the art. Preferably, the product is
molded under pressure and heat ("cooked") using, for example, a
hydraulic press with heated platens. The platens may be heated by
any means known in the art, for example, steam, oil, or
electricity. If the product is cold-cured, little pressure is
generally used. Preferably, the molding is performed at from about
200.degree. F. to about 400.degree. F., more preferably, from about
300.degree. F. to about 400.degree. F. The conditions under which
the molding is performed--for example, the amount of binder, type
of binder, time, pressure, and temperature at which the product is
molded--affects the properties of the product. For example,
increasing the molding pressure typically increases the tensile
strength of the product. Preferably, the pressure is from about 75
psi to about 500 psi, more preferably from about 150 psi to about
300 psi. The molding time depends on a variety of factors including
the particular binder used, the temperature of the raw materials,
the temperature of the platens, and the thickness of the product.
Determining particular conditions required to achieve the desired
properties is within the knowledge of the skilled artisan in view
of the disclosure herein.
Preferred embodiments of the processes disclosed herein preferably
have one or more advantages over known processes. The total amount
of binder used may be reduced, which reduces the cost. Embodiments
in which the amount of binder is reduced in the second step have
reduced processing times, thereby increasing the rate of
production. Products made according to the processes disclosed
herein have increased tensile strength compared to products made
using the same amount of binder using known processes.
Without being bound by any theory, this treatment step has two
beneficial effects. First, the binder reacts with water in the
rubber thereby drying the rubber. Second, the binder coats the
rubber particles with polyurethane. When additional binder is added
in the second step, it binds to polyurethane instead of rubber,
which leads to the higher tensile strengths observed in the
finished products made by the disclosed processes.
Treated Rubber
Ground rubber was preheated to 150.degree. F. and combined with 1%
MDF-403 binder (Ryvec, Inc., Anaheim, Calif.) with constant mixing
in a jacketed ribbon mixer equipped with a double spiral ribbon.
Treatment was complete in about 15 minutes.
Animal Mats
100 lb of 1% treated rubber was mixed with 15 lb MD-400 binder
(Ryvec, Inc., Anaheim, Calif.) for 1 minute. The mixture was placed
into molds (3/4".times.4'.times.8') and leveled. The molds were
placed into a press with heated platens for 7 minutes at 150 psi
and 280.degree. F. The mats reached full tensile strength in about
24 hours.
Comparative Results
These results compare finished rubber mats made by the disclosed
process and by the commercial process. For each set of conditions,
three 1/4".times.6".times.6" mats were molded, and three samples
were cut from each mat for tensile strength testing (nine samples
for each set of conditions). The "Rubber" column indicates the
conditions under which the treatment step was performed. The
"Binder," "Temp.," "Time," and "Mold Pressure" columns indicate the
conditions under which the forming step was performed. The "Tensile
Strength" column indicates the average tensile strength for mats
made under the specified conditions.
Table 1 compares the effect of using different amounts of binder in
the treatment step. For the treated rubber, the amount of binder
used in the forming step was adjusted such that the total amount of
binder used was 2.5%. For the standard and dried rubber, 3% binder
was used. The rubber used in these tests contained large amounts of
nylon. The treatment and forming steps use different binders in
these examples.
TABLE 1 Mold Tensile Rubber.sup.a Binder.sup.b Temp. Time Pressure
Strength 1 Standard 3.00% 300.degree. F. 2 min 150 psi 215 psi 2
Dried 3.00% 300.degree. F. 2 min 150 psi 224 psi 3 0.25% Treated
2.25% 300.degree. F. 2 min 150 psi 249 psi 4 0.50% Treated 2.00%
300.degree. F. 2 min 150 psi 261 psi 5 1.00% Treated 1.50%
300.degree. F. 2 min 150 psi 265 psi 6 1.50% Treated 1.00%
300.degree. F. 2 min 150 psi 264 psi .sup.a "Standard" refers to
untreated rubber; "Dried" refers to rubber dried at 250.degree. F.
for 15 min.; "Treated" refers to rubber treated with the stated
percentage of MD-403 binder (Ryvec, Inc., Anaheim, CA) for 15 min.
at 150.degree. F. .sup.b MD-400 binder (Ryvec, Inc., Anaheim,
CA).
As expected, mats molded from dried rubber (Example 2) are stronger
than those molded from standard rubber (Example 1). As shown in
Example 3, as little as 0.25% of binder in the treatment step
increased the tensile strength of the product compared to the
product made from either the standard or dried rubbers. The
difference between tensile strength advantage for the treated
rubber is probably greater than that indicated in this table
because the total amount of binder used in the Examples 1 and 2 was
3%, while in the total amount used in Examples 3 to 6 was only
2.5%. The tensile strength of the product increases with the amount
of binder used in the treatment step, up to about 1% binder under
these conditions (compare Example 4 with Example 5).
Table 2 compares the tensile strengths of mats made from three
types of rubber--standard, dried, and 1% treated--under varying
molding conditions. The rubber in these tests contained less nylon
than the rubber used in the tests described in Table 1.
TABLE 2 Mold Tensile Rubber.sup.a Binder.sup.b Temp. Time Pressure
Strength 7 Standard 3% 300.degree. F. 2 min 150 psi 229 psi 8 Dried
3% 300.degree. F. 2 min 150 psi 273 psi 9 Treated 1.5% 300.degree.
F. 2 min 150 psi 302 psi 10 Standard 3% 300.degree. F. 2 min 220
psi 237 psi 11 Dried 3% 300.degree. F. 2 min 220 psi 283 psi 12
Treated 3% 300.degree. F. 2 min 220 psi 379 psi 13 Treated 2%
300.degree. F. 2 min 220 psi 351 psi 14 Treated 1.5% 300.degree. F.
2 min 220 psi 343 psi 15 Treated 1% 300.degree. F. 2 min 220 psi
282 psi 16 Standard 3% 300.degree. F. 2 min 500 psi 289 psi 17
Dried 3% 300.degree. F. 2 min 500 psi 346 psi 18 Treated 3%
300.degree. F. 2 min 500 psi 529 psi 19 Standard 3% 400.degree. F.
40 sec 75 psi 147 psi 20 Dried 3% 400.degree. F. 40 sec 75 psi 179
psi 21 Treated 2% 400.degree. F. 30 sec 75 psi 232 psi 22 Treated
1.5% 400.degree. F. 30 sec 75 psi 200 psi 23 Treated 1.5%
400.degree. F. 20 sec 75 psi 169 psi .sup.a "Standard" refers to
untreated rubber; "Dried" refers to rubber dried at 250.degree. F.
for 15 min.; "Treated" refers to rubber treated with 1% MD-403
binder (Ryvec, Inc., Anaheim, CA) for 15 min, at 150.degree. F.
.sup.b MD-400 binder (Ryvec, Inc., Anaheim, CA).
The tensile strength of the product increased in Examples 7, 8, and
9 for standard, dried, and treated rubber, respectively. Again, the
total binder content in Example 9, 2.5%, was less that in Examples
7 and 8, 3%, and the Example 9 product is stronger. A direct
comparison at constant binder content and identical molding
conditions is provided in Examples 10, 11, and 13. Again, the
treated rubber (Example 13) gives a stronger product than the dried
rubber (Example 11), which in turn is stronger than standard rubber
(Example 10).
The foregoing examples serve to illustrate the preferred embodiment
and are not intended as limitations. Modifications and variations
of the preferred embodiment will be apparent to those skilled in
the art without departing from spirit of the invention, the scope
of which is limited only by the appended claims.
* * * * *